Neutrino search in Auger Ricardo A. Vázquez University of Santiago de Compostela, Spain for the Pierre Auger collaboration Beijing, April 2006

1.The Pierre Auger Observatory 2. Neutrino Search: 3. Fluorescence Detector (FD) Search 4. Surface Detector Search 5. Conclusions

The Pierre Auger Observatory Aims at measuring The Highest Energy Cosmic Rays Energy Spectrum - Direction – Composition - Anisotropy Hybrid detection: Fluorescence and Surface detectors Two Large Air Shower Detectors Mendoza Province, Argentina (under construction) Colorado, USA

The Auger Collaboration Participating Countries ArgentinaMexico Australia Netherlands Bolivia * Poland Brazil Slovenia Czech RepublicSpain France United Kingdom Germany USA ItalyVietnam * * Associate 63 Institutions, 369 Collaborators

Surface Array 100% duty cycle Uniform sky coverage Simple robust detectors Mass determination using rise time, & muon/em Fluorescence Detector Calorimetric energy measurement Direct view of shower development: Xmax measurement, mass determination Good angular resolution (< 1 o ) Hybrid concept

Advantages Independent measurement techniques allow cross calibration and control of systematics More reliable energy and geometry reconstruction Primary mass Hybrid concept: Surface Detector Array and Fluorescence Detectors Two observatories: allow full sky coverage

Auger Southern Site Mendoza province, Argentina

The Observatory Plan Surface Array 1600 detector stations 1.5 km spacing 3000 km 2 Fluorescence Detectors 4 Telescope enclosures 6 Telescopes per enclosure 24 Telescopes total

The Auger Surface Detector Three 8” PM Tubes Plastic tank White light diffusing liner 12 m 2 of de-ionized water Solar panel and electronic box Comm antenna GPS antenna Battery box

Fluorescence Detector Building at Los Leones

The Fluorescence Detector 3.4 meter diameter segmented mirror Aperture stop and optical filter 440 pixel camera

Atmosphere calibrated (movable) light sources cloud monitors LIDAR lasers balloon sondes 2. Intl Workshop Liebenzell Castle Dec 11-14

On-line monitoring(Big Brother) Detector elements are monitorized every 10 mins. Alarms inform about anomalies.

Auger Center Building

Detector Assembly Building Cerenkov detector tanks being prepared for deployment The Auger Campus

The communications system Rigging the antennas

Array status by the End tanks deployed ~100% duty cycle

905 surface detector stations deployed Three fluorescence buildings complete each with 6 telescopes End of 2005

Status of the March 2006 ~ 1000 stations

The First Data Set Collection period – 1 January 2004 to 5 June 2005 Zenith angles º Total acceptance – 1750km 2 sr yr (~ AGASA) Surface array events (after quality cuts) Current rate - 18,000 / month Total -~180,000 Hybrid events (after quality cuts) Current rate – 1800 / month Total ~ Cumulative number of events January 04 July 04 January 05

Official First FD Event

Surface Detector First 4 – fold event – 12 August

Flash ADC traces Lateral density distribution Hybrid Event Θ~ 30º, ~ 8 EeV

Fitted Electromagnetic Shower from Fly's Eye 1985 Time μ sec Angle Χ in the shower-detector plane Hybrid Event Θ~ 30º, ~ 8 EeV Tanks Pixels

Example Event Θ~ 48º, ~ 70 EeV Flash ADC traces Lateral density distribution Typical flash ADC trace Detector signal (VEM) vs time (ns) PMT 1 PMT 2 PMT 3

Lateral density distribution Surface Detector Event Θ~ 60º, ~ 86 EeV Flash ADC traces Flash ADC Trace for detector late in the shower PMT 1 PMT 2 PMT 3

Hybrid event

Performance: Resolution of Core Position Hybrid – SD only core position Hybrid Data Laser Data Core position resolution –Hybrid: < 60 m Surface array: ~150 m Laser position – Hybrid and FD only (m) Entries 501 Mean 5.8 ± 6.5 m RMS 147 m Entries 501 Mean 68 ± 8 m RMS 173 m

Performance: Angular Resolution Surface array Angular resolution (68% CL) < 2.2º for 3 station events (E< 3EeV, θ < 60º ) < 1.7º for 4 station events (3<E<10 EeV) 10 EeV) Hybrid Angular resolution (68% CL) 0.6 degrees (mean) Hybrid-SD only space angle difference Hybrid Data Angle in laser beam /FD detector plane Laser Beam Entries 269 σ(ψ) =1.24º

Energy Determination and the Spectrum The detector signal size at 1000 meters from the shower core - called the ground parameter or S(1000) - is determined for each surface detector event using the lateral density function. S(1000) is proportional to the primary energy. The energy scale is based on fluorescence measurements without reliance on a specific interaction model or assumptions about the composition. Zenith angle ~ 48º Energy ~ 70EeV

Energy Determination and the Spectrum The energy converter: Compare ground parameter S(1000) with the fluorescence detector energy. Transfer the energy converter to the surface array only events. Log S(1000) Log (E/EeV) 10EeV 1 EeV Hybrid Events Strict event selection: track length >350g/cm2 Cherenkov contamination <10%

Auger Energy Spectrum  E/E~30%  E/E~50% ICRC 2005 spectrum

Neutrino search in Auger FD search –Auger can detect neutrinos directly with the fluorescence detector SD search –Deep inclined (neutrino) showers should have a different time structure (risetime/falltime), curvature, etc. and electromagnetic component Different strategies

M. Roth et al., Karlsruhe FD search

M. Roth, Karlsruhe

a real vertical event (20 deg) Noise ! doublet SD search

a real horizontal event (80 deg) “single” peaks : fast rise + exp. light decay (  ~ 70 ns) accidental background signals are similar

Simulated   + ( 5.1)  0 (16.1)  1800 m above ground

EM signal in shower plane Proton 1 EeV θ = 80 deg x shower plane [m] y shower plane [m] [VEM] ρ, ε → S μ,EM 3167 g/cm g/cm g/cm g/cm g/cm g/cm g/cm g/cm g/cm g/cm g/cm g/cm g/cm g/cm 2 X injection J. Alvarez-Muniz Downgoing showers

Controlled calculation: strategy We need ΔX where neutrino triggers are expected → Effective volume Calculate size of active region (where S EM >S threshold )

2D EM signal maps at ground EM signal [VEM] x [km] y [km] Proton, E = eV, h int = 0 m θ = 90.1 degθ = 90.5 degθ = 91 degθ = 110 degθ = 92 degθ = 93 degθ = 95 degθ = 100 degθ = 105 deg AIRES + SIBYLL 2.1 Fixed proton interaction height h int = 0 m J. Alvarez-Muniz Upcoming showers

2D EM signal maps at ground EM signal [VEM] x [km] y [km] Proton, E = eV, θ = 91 deg. h int = 0 m AIRES + SIBYLL 2.1 h int = 50 mh int = 100 mh int = 300 mh int = 500 mh int = 1000 mh int = 3000 m Fixed zenith angle θ = 91 deg. J. Alvarez-Muniz

Event Event  = 71.5±0.02  = -57.2±0.02 E ~ 50 EeV R= 22.9 km  /dof =2.4 NTanks =48  = 77.1± 0.01  = ± 0.01 E ~ 30 EeV R= km  /dof =1.81 NTanks = 59 Some events

Event  = 87.6  = E ~ 30 EeV  /dof =1.7 NTanks = 37

Post-San Valentin day event Event  = 83  = -102 E ~ 40 EeV  /dof =2.3 NTanks = 61

10% 50% Risetime is defined as the time from 10% - 50% of the integrated pulse. Falltime time from 50% - 90% Risetime/Falltime S [VEM] 90 %

Falltime vs Risetime (no cuts) All stations θ ≥ 70 deg. θ ≤ 45 deg. J. Alvarez-Muniz

Falltime vs Risetime (1 cut) S ≥ 15 VEM θ ≤ 45 deg. θ ≥ 70 deg.

Falltime vs Risetime (2 cuts) S ≥ 15 VEM & r ≥ 500 m θ ≥ 70 deg. θ ≤ 45 deg. Neutrino candidates should have θ ≥ 70 deg and should show up here. No events up to now!

No θ ≥ 70 deg. Candidates looking like (0,45) deg. events. No deep inclined events starting at vertical depths between 870 and 870/cos45 = 1230 g/cm 2 (from the detector) => target volume => limit on deep showers.

L Cazon, RAV, A. Watson, E. Zas (Ap Phys 2004) Curvature analysis

Arrival Time of first muon (& average) -like delay large p-like delay: small (flat) L. Cazon, RAV, E. Zas

footprint analysis Variables defined from the footprint (in any configuration, even aligned) length L and width W (major and minor axis of the ellipsoid of inertia) “speed” for each pair of stations (distance/difference of time) major axis titi tjtj d ij P. Billoir & O. Blanch

candidate selection 2. Discriminating variables cuts: L/W > < av. Speed < 0.31 r.m.s. < 0.08 Search for long shaped configurations, compatible with a front moving horizontally at speed c, well contained inside the array (background: vertical or inclined showers, d/Dt > c ) from years : no real event survived…

Auger sensitivity Points: 1 event / year / decade of energy “pessimistic”  energy loss uncertainty range GRB TD AGN GZK preliminary P. Billoir & O. Blanch

3C2 & 4C4 2C1 & 3C2 & 4C4 2C1 & 4C2 3C1 & 4C2 not saturated yet at eV compacity of the trigger matters ! L. Nellen, V. Van Elewyck & RAV Log(E/eV) Understanding the background: HAS Optimal trigger?

Conclusions -The Pierre Auger Observatory is performing well and steadily taking data -Due to the Hybrid characteristics several neutrino searches are possible -Need to understand the background, model dependence on the aperture, systematics,…. -We will keep looking for neutrinos !